Traffic is filled with injunctive norms, telling drivers what to do and what not to do. But the descriptive norm is often saying something else - and saying it louder. The most common example is the speed limit. The law on many U.S. highways is 65 miles per hour, but a norm has gradually emerged that says anything up to 10 miles per hour above that is legal fair game. Raise the speed limit, and the norm tends to shift; driving the speed limit starts to seem hazardous.
In Australia the current Australian Design Rules for vehicles say speedometers aren't allowed to under-read, so the police can book you if you are 1 km/h over the speed limit if they like. I don't know what tolerance they actually use, but driving at the speed limit is no problem here for other drivers.
The chapter in the book also talks about tipping, which seems like a form of corruption to me. "If you want to know how corrupt a given country is, you may not need a big police sting. You could just look at how regularly its citizens tip." However, it seems like "the norm" to people living in tipping countries and they often defend it (just like Australians often defend mandatory bicycle helmet laws).
One of the least corrupt countries in the world is Finland, where your traffic fine is proportional to your income.